Superjunction Power MOSFET Source Region Placement
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Solution Overview
Problem
The existing power MOSFETs face challenges in achieving large breakdown strength due to the long distance between trenches and high concentration diffusion regions, leading to parasitic npn transistor activation during avalanche breakdown or reverse recovery, which increases the likelihood of di/dt breakdown.
Innovation Solution
A power semiconductor device with a super junction structure is developed, featuring alternately formed n-type and p-type columnar regions, where the first conductive-type high concentration diffusion region is formed only between the trench and the metal plug closest to it, reducing the distance and area of the boundary surface, thereby minimizing parasitic npn transistor activation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If metal plugs with small diameter are formed between adjacent trenches to downsize the device, then the device size is reduced, but the distance between trenches and high concentration diffusion regions increases leading to parasitic npn transistor activation
Solution Approach 1:
The device structure is segmented into alternating n-type and p-type columnar regions (superjunction structure), with source regions positioned only in n-type regions adjacent to trenches. This segmentation allows multiple contact holes to be formed between trenches without increasing the distance from trenches to high concentration diffusion regions, as each n-type columnar region is independently configured with its own source region and contact holes.
Solution Approach 2:
High concentration diffusion regions (source regions) are locally positioned only in n-type columnar regions that are adjacent to trenches, rather than uniformly distributed. This local quality enhancement ensures that wherever a trench exists, the adjacent n-type region has a source region with contact holes immediately available, minimizing the distance for carrier collection and preventing parasitic transistor activation.
2Reliability
If the distance between trenches and high concentration diffusion regions is reduced to prevent parasitic transistor activation, then breakdown strength is improved, but the device layout becomes more complex
Solution Approach 1:
The alternating n-type and p-type columnar regions create natural segments where source regions are only formed in n-type regions adjacent to trenches. This segmentation automatically ensures short distances between trenches and high concentration diffusion regions without requiring complex layout design, as the superjunction structure itself provides the optimal configuration.
Solution Approach 2:
The n-type columnar regions serve multiple functions: they act as drift regions for voltage blocking, as localized regions for source region formation, and as pathways for carrier collection. This multi-functionality allows the same structural element to satisfy multiple requirements simultaneously, including maintaining short distances to trenches while preserving device performance.
3Reliability
If source regions are formed in all regions between trenches to minimize carrier travel distance, then breakdown strength improves, but parasitic npn transistor activation increases due to increased boundary surface area
Solution Approach 1:
Source regions are selectively formed only in n-type columnar regions that are adjacent to trenches, rather than in all regions between trenches. This local quality differentiation ensures that carrier travel distance is minimized only where necessary (near trenches where avalanche breakdown occurs), while avoiding the creation of additional boundary surfaces in p-type regions that would increase parasitic transistor activation.
Solution Approach 2:
The p-type columnar regions, which would otherwise be potential sites for source region formation and parasitic transistor activation, are converted into beneficial elements by forming p-type base regions that extend into them. These p-type regions act as barriers that prevent hole injection into n-type regions, thereby suppressing parasitic npn transistor activation while the adjacent n-type regions still provide the necessary short carrier paths.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This configuration enhances breakdown strength by reducing the distance carriers need to travel and minimizing the boundary surface area, resulting in reduced avalanche breakdown and di/dt breakdown occurrences, while maintaining a downsized and cost-effective design.
Implementation Method 1
At the time of the occurrence of an avalanche breakdown or reverse recovery of a body diode, holes which are generated at a bottom portion of the trench
Data Source
AI summary
A power semiconductor device of the present invention includes: a semiconductor base body which has a super junction structure formed of a plurality of first conductive-type columnar regions and a plurality of second conductive-type columnar regions; a plurality of trenches; gate insulation films; gate electrodes; an interlayer insulation film; contact holes formed such that two or more contact holes are formed between two trenches disposed adjacently to each other; metal plugs formed by filling the inside of the contact holes with metal; and an electrode, wherein a first conductive-type high concentration diffusion region is formed only between the trench and the metal plug disposed closest to the trench between each two trenches disposed adjacently to each other. According to the power semiconductor device of the present invention, it is possible to provide a power semiconductor device which satisfies a demand for reduction in cost and downsizing of electronic equipment, and has a large breakdown strength.